The exemplary embodiment relates to the printing arts. It finds particular application in connection with the transport of print media through a paper path intersection within a printing system, and will be described with particular reference thereto. However, it will be appreciated that the exemplary embodiment finds application in other systems.
Electronic image forming systems, such as printing systems, typically employ an input terminal which receives images in digital form and conversion electronics for converting the image to image signals or pixels. For example, the printing system may include a scanner for scanning image-bearing documents or be connected to a computer network which supplies the digital images. The image signals are stored and are read out successively to a marking engine for formation of the images and transfer of the images to a print medium, such as sheets of paper.
In typical xerographic (electrophotographic) printing systems, such as copy machines and laser beam printers, the marking engine includes a photoconductive insulating member, which is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a marking material. Generally, the marking material comprises toner particles adhering triboelectrically to carrier granules, which is often referred to simply as toner. The developed image is subsequently transferred to the paper. The fusing of the toner image onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a complementary color. The single color toner images are successively transferred to the paper to create a multi-layered toner image on the paper. The multi-layered toner image is then permanently affixed to the paper in the fusing process.
Printing systems have been developed which employ multiple marking engines for providing higher print outputs by distributing a print job among the marking engines. These systems may include several black, process (or full) color, and/or custom color (single color or monochrome) marking engines for printing of selected pages within a print job. A conveyor system transports the sheets of print media within the printing system. Decision gates can be used to control the flow of sheets through the points where one pathway merges with another, to prevent collisions between merging sheets. The gate is controlled to open when there is a sufficient inter-document gap for an incoming sheet to merge with the sheets already on a pathway.
The timing of the decision gate, its actuation, and return for a subsequent sheet are often critical for efficient operation of the printing system. However, the decision gate includes mechanical components, such as solenoids, linkages, springs, and a gate which can wear and fail to function over time resulting in lower reliability of the system. In addition, the gate tends to create a catch point area where the sheets may jam. Typical jam clearance usually results in a shutdown of the system. Further, the gate takes a finite amount of time to operate, which may limit the maximum productivity of the printing system, particularly when the gate is in frequent use. Another problem arises from merging the output of multiple marking engines. The relatively lower speed output of each marking engine is generally merged into an accelerated, high velocity main media pathway.